Method and device adapted for use in the placing of a suction anchor with an attached anchor chain or similar on the ocean bed

ABSTRACT

A method and a device for use in the placing of a suction anchor ( 1 ) with an attached anchor chain ( 2 ) on the ocean bed. The suction anchor ( 1 ) and the anchor chain ( 2 ) are to be lowered separately to the ocean bed, and be connected at the ocean bed without any use, worth mentioning, of mechanically movable parts or closing mechanisms, the process is to take place by means of gravity and in as few operations and with as few pieces of expensive utility equipment as possible. This is done in that the suction anchor ( 1 ) and the anchor chain ( 2 ) are connected by means of a guiding element ( 6 ) with a lower locking element ( 7 ) arranged thereto, and a connecting element ( 3 ). The connecting element ( 3 ) is positioned at the lower end of the anchor chain ( 2 ) and adapted for insertion into the guiding and locking elements ( 6, 7 ). The guiding and locking elements ( 6, 7 ) are positioned on the side wall ( 12 ) of the suction anchor. The connecting takes place in that the connecting element ( 3 ) is lowered into the guiding and locking elements ( 6, 7 ) first. Then the upper end of the connecting element ( 3 ) is pulled outwards from the suction anchor ( 1 ), so that the connecting element ( 3 ) is brought into a position in which the longitudinal axis of the connecting element ( 3 ) is concentric with the longitudinal axis of the bore ( 9 ) of the locking element. The operation is completed in that the connecting element ( 3 ) is pulled outwards from the suction anchor ( 1 ) along the direction of the longitudinal axis of the bore ( 9 ) of the locking element, until the locking piece ( 4 ) of the connecting element ( 3 ) engages the locking element ( 7 ).

The invention relates to a method and a device adapted for s, use in theplacing of a suction anchor with an attached anchor chain or similar onthe ocean bed, said suction anchor being lowered first without theanchor chain, and secured by suction to the ocean bed, after which thelower end of the anchor chain is lowered and connected to the suctionanchor.

Suction anchors with associated anchor chains are used when floatinginstallations of different kind are to be anchored to the ocean bed.Earlier it was common for the suction anchor and the associated anchorchain to be transported off shore and lowered to the ocean bedcollectively. This resulted in very high costs since the suction anchorand the associated anchor chain have a great weight, often more than athousand tons, and take up a lot of space, so that large surface vesselsand heavy crane equipment were needed. The costs were reduced somewhatthrough the gradual change to transporting and lowering of the suctionanchor and anchor chain separately. This involves reduced costs withrespect to the surface vessel and crane equipment, but it has turned outthat the reduction is balanced, to a large extent, by new costs that didnot accrue when the suction anchor and the anchor chain were transportedand lowered collectively. Of such costs may be mentioned that it will benecessary to provide a submarine vehicle with the equipment necessaryfor the connection of the suction anchor and the anchor chain on theocean bed, that a far more complex device must be provided forconnecting the suction anchor and the anchor. chain than when theconnection is carried out before the lowering, that the work takes moretime, etc. Another important drawback is that the known devices forconnecting the suction anchor and the anchor chain on the ocean bed, arehighly complicated constructions that give rise to many faults anddelays during the connection.

The main object of the present invention is to provide a method and adevice of the above type, wherein the suction anchor and the anchorchain are lowered to the ocean bed separately, and wherein theconnecting of the suction anchor and the anchor chain can be carried outwithout the use of an expensive submarine vehicle performing the actualconnecting. Other objectives are that the connecting is to take placewithout any use, worth mentioning, of mechanically movable parts orclosing mechanisms, that the connecting shall be carried out withoutfaults and by means of gravity, and in as few operations and otherwisewith as few pieces of expensive utility equipment as possible.

As appears from the characterizing part of the present independent claimconcerning the above method, this is realized by connecting the suctionanchor and the lower end of the anchor chain in the following steps:

i) the lower end of the anchor chain is lowered into a verticallyextending guiding element with a lower locking element arranged thereto,the guiding and locking elements being provided externally on the sidewall of the suction anchor and formed with a bore each, arranged so thatthe longitudinal axes form an acute angle between themselves, and thelower end of the anchor chain has a preferably rod-like connectingelement arranged thereto;

ii) the upper end of the connecting element is pulled outwards from thesuction anchor, so that the connecting element is brought into aposition, in which the longitudinal axis of the connecting element isconcentric with the longitudinal axis of the bore of the lockingelement; and

iii) the connecting element is pulled outwards from the suction anchorin the direction along the longitudinal axis of the bore of the lockingelement until the lower end of the connecting element engages thelocking element of the suction anchor, the lower end of the connectingelement being formed as a locking piece with a cross-sectional shapeadapted to the bore of the locking element.

As appears from the characterizing part of the present independent claimconcerning the above device, through the connection of the suctionanchor and the anchor chain, by means of a vertically extending guidingelement provided with a lower locking element and a preferably rod-likeconnecting element, the connecting element being adapted for insertioninto the guiding and locking elements and engagement with the lockingelement; through the provision of the guiding and locking elementsexternally on the side wall of the suction anchor, and theirconfiguration with a bore each, arranged so that the longitudinal axesform an acute angle between themselves, and through the positioning ofthe connecting element on the lower end of the anchor chain and itsconfiguration with a lower locking piece, the locking piece being of across-sectional shape adapted to the cross-sectional shape of the boreof the locking element. Other advantageous features of the inventionappear from the present dependent claims and otherwise from thespecification.

In the following part of the specification and with reference to the setof figures, an embodiment of the invention will be explained,

FIG. 1 showing a schematic section of a vertical section through thepresent suction anchor and anchor chain. As shown, the suction anchor isequipped with an upper guiding element and a lower locking element, andthe anchor chain with a lower connecting element. The suction anchor hasearlier been lowered and secured by suction to the ocean bed. The anchorchain, on the other hand, has been lowered into a position, in which theconnecting element hangs above the guiding and locking elements prior toconnection;

FIGS. 2-3 showing the same section as that in FIG. 1, apart from theconnection having been initiated, and the connecting element having beenlowered into the guiding and locking elements;

FIG. 4 showing the same section as that in FIG. 1, except thatadditionally the connecting element has been lowered through a recess ofthe locking element, and the connecting element has been pushedlaterally outwards and into a slit in the guiding element by means of alocking piece at the lower end of the connecting element and a guidesurface of the recess of the locking element;

FIGS. 5-7 showing the same section as that in FIG. 1, except that theupper end of the connecting element is pulled laterally outwards fromthe suction anchor, or is pulled into a position, in which thelongitudinal axis of the connecting element is concentric with alongitudinal axis of a bore of the locking element;

FIG. 8 showing the same section as that in FIG. 1, except that theconnecting element is pulled out in the direction along the longitudinalaxis of the bore of the locking element, so that the locking piece ofthe connecting element is brought into engagement with the bore of thelocking element; and

FIG. 9 showing a sectional view of a horizontal section, with enlargeddetails, through the suction anchor and the guiding element.

The present invention relates to a suction anchor 1 with an anchor chain2 or similar arranged thereto. The suction anchor is placed on the oceanbed and is preferably used in the anchoring of floating installations orsimilar. The necessary number of suction anchors must be adjusted to therespective installation. The positioning on the ocean bed is carried outin that the suction anchor 1 is lowered first from a suitable surfacevessel without the associated anchor chain 2, and is secured by suctionto the ocean bed. Then the anchor chain 2 is lowered from the vesseluntil its lower end reaches and is connected to the suction anchor 1.After the connection, provision is normally provided for a lower portionof the anchor chain to be laid on the ocean bed, laterally outwards fromthe suction anchor 1.

The connection of the suction anchor 1 and the anchor chain 2 isimplemented by means of a guiding element 6 of an essentially verticalextent, provided with a lower locking element 7, and a rod-likeconnecting element 3. The connecting element 3 is adapted for insertioninto the guiding and locking elements 6, 7, and is brought intoengagement with the locking element 7. The guiding and locking elements6, 7 are positioned externally on the side wall 12 of the suctionanchor, and they are formed with a bore 8, 9 each. The bore 8 of theguiding element extends vertically through the guiding element 6, and itis equipped with an upper funnel-shaped element which is helpful whenthe connecting element 3 is to be inserted into the guiding element 6.The bore 9 of the locking element extends from a lateral edge of thelocking element 7 opposite the bore 8 of the guiding element and slopestowards the bore 8, so that the longitudinal axes of the bores 8, 9 ofthe guiding and locking elements form an acute angle between themselves.The connecting element 3 may be attached to the lower part of the anchorchain 2 by means of a shackle-like securing means 5, and it is formedwith a lower locking piece 4. The locking piece 4 has a cross-sectionalshape adapted to the cross-sectional shape of the bore 9 of the lockingelement, so that the locking piece is brought into engagement with thebore 9 of the locking element during the final stage of the connecting.Further, the locking element 7 is formed with a recess 14 which isadapted so, that the locking piece 4 of the connecting element 3 may becarried from the bore 8 of the guiding element into the bore 9 of thelocking element. The recess 14 of the locking element has an extentwhich makes the bores 8, 9 of the guiding and locking elementsconnected.

The guiding element 6 is formed with a vertically extending slit 10associated with the bore 8 of the guiding element. The slit 10 of theguiding element is closed on the side that faces away from the bore 8 ofthe guiding element, by means of an end piece formed with a verticallyextending rupture line 13, e.g. in the form of a V-shaped milling. Thelocking element 7 is formed with a guide surface 11 adapted so, that inthe connecting, the connecting element 3 can be displaced into the slit10 of the guiding element, or the locking piece 4 may be brought intoengagement with the bore 9 of the locking element. The guide surface 11is positioned adjacent to the recess 14 of the locking element and thebore 9 of the locking element. Further, the guide surface 11 is formedwith a first portion sloping downwards, and a second portion slopingupwards, seen in relation to the longitudinal axis of the bore 8 of theguiding element. These are connected to an intermediate rounded portion.The connecting element 3 is displaced into the slit 10 of the guidingelement when the locking piece 4 is displaced along and down the formerportion of the guide surface 11. The locking piece 4 is brought intoengagement with the bore 9 of the locking element when differentportions of the locking piece 4 are displaced along different portionsof the guide surface 11 or the bore 9 of the locking element.

Coarse particles can cause great damage to the anchor chain, if thelower end at the connecting element 3 comes to be positioned under theocean bed. This implies that the connecting element 3 should be formedwith a length that makes it possible for the anchor chain 2 to bepositioned above the ocean bed. The heave of the waves may cause damageduring the connecting of the suction anchor 1 and the anchor chain. Suchdamage can be avoided if a portion of the anchor chain is coiled up andfixed by means of a not shown lashing, which is arranged so that itbreaks into pieces by undesirable heave of the waves. Thereby isensured, that after the lashing has been broken, the coiled up part ofthe anchor chain may equalize the heave of the waves. Otherwise it isapparent that the anchor chain 2 may be replaced by another suitablemooring means, and be attached to the connecting element 3 in adifferent manner than by the shown shackle-like securing means 5.Neither is there anything to prevent the funnel at the bore 8 of theguiding element from being provided with a not shown cover or similar,which will prevent the entrance of mass from the ocean bed, but willallow the connecting element 3 to be inserted into the guiding element6.

The connecting is monitored by a minor and remotely controlled submarinevehicle, not shown, so that i.a. the connecting element 3, hanging downfrom the lower end of the anchor chain 2, may be manoeuvred in towardsthe funnel at the upper end of the guiding element 6. Then, when theconnecting element 3 is brought into correct position above the funnel,more anchor chain 2 is let out from the surface vessel. Thereby theconnecting element 3 is lowered into the bore 8 of the guiding element.During the final stage of its being lowerered into the guiding element6, the locking piece 4 of the connecting element 3 abuts and is loweredalong the first portion of the guide surface 11 of the locking element7. This entails that the connecting element 3 is passed sideways intothe slit 10 of the guiding element. When the lowering has beencompleted, the upper end of the connecting element 3 is pulled laterallyoutwards from the suction anchor until the longitudinal axis of theconnecting element 3 is in a position concentric with the longitudinalaxis of the bore of the locking element 9. This happens in the way thatthe connecting element 3 is torn out through the end piece of the slit10 of the guiding element along the rupture line 13. As the upper end ofthe connecting element 3 is being pulled out, different parts of thelocking piece 4 will abut different parts of the guide surface 11 andparts of the bore 9 of the locking element, so that said parts almostact as a rotary joint for the connecting element 3. The connecting endsby the connection element 3 being pulled outwards from the suctionanchor 1 in the direction along the longitudinal axis of the bore 9 ofthe locking element, until the locking piece 4 at the lower end of theconnecting element 3 engages the bore 9 of the, locking element. Thesubmarine vehicle may be used to check that the connecting element 3 hasreached the bottom inside the guiding and locking elements 6, 7, thatthe upper end of the connecting element 3 has been pulled out far enoughin the lateral direction from the suction anchor 1, and that theconnecting element 3 has been pulled out sufficiently far in thedirection along the longitudinal axis of the bore 9 of the lockingelement.

What is claimed is:
 1. A method of placing a suction anchor with anattached anchor tether on the ocean bed, including lowering the suctionanchor and securing the anchor by suction to the ocean bed, andthereafter connecting a lower end of the anchor tether to the suctionanchor, the method comprising: lowering the lower end of the anchortether into a vertically extending guiding element with a lower lockingelement arranged thereto, the guiding and locking elements beingpositioned on the exterior of a side wall of the suction anchor andformed with a bore and arranged so that the longitudinal axes form anacute angle, the lower end of the anchor tether having a rod-likeconnecting element arranged thereto; pulling an upper end of theconnecting element outwards from the suction anchor so that theconnecting element is generally brought into a position in which thelongitudinal axis of the connecting element is concentric with thelongitudinal axis of the bore of the locking element; and pulling theconnecting element outwards from the suction anchor and toward thelongitudinal axis of the bore of the locking element until a lower endof the connecting element engages the locking element of the suctionanchor, the lower end of the connecting element being formed as alocking piece with a cross-sectional shape adapted to the bore of thelocking element.
 2. A method as defined in claim 1, wherein when thelocking piece is lowered into the locking element, the connectingelement is displaced sideways out from the suction anchor and into aslit formed in the guiding element, the locking element being formedwith a guide surface for the locking piece.
 3. A method as defined inclaim 1, wherein when the upper end of the connecting element is pulledoutwards from the suction anchor, the connecting element is torn throughan end piece of a slit of the guiding element, the end piece beingformed with a vertically extending rupture line.
 4. A method as definedin claim 1, wherein when the upper end of the connection element ispulled outwards from the suction anchor, the locking piece is retainedin the locking element, parts of the locking piece first bearing on theguide surface of the locking element and then on parts of the bore ofthe locking element.
 5. A method as defined in claim 1, wherein aportion of the anchor tether is coiled up and fixed by lashing arrangedto break into pieces on the occurrence of wave heave when connecting ofthe suction anchor and the anchor tether.
 6. An assembly using a suctionanchor with an anchor tether arranged to be placed on the ocean bed,wherein the suction anchor is lowered and secured by suction to theocean bed, after which a lower end of the anchor tether is lowered andconnected to the suction anchor, the assembly further comprising: thesuction anchor and the anchor tether being connected by a verticallyextending guiding element with a lower locking element arranged thereto;a rod-like connecting element adapted for insertion into the guiding andlocking elements and for engagement with the locking element, in thatthe guiding and locking elements are positioned externally on the sidewall of the suction anchor and formed with a bore each arranged so thattheir longitudinal axes form an acute angle; and the connecting elementbeing positioned at the lower end of the anchor tether and formed with alower locking piece, the locking piece having a cross-sectional shapeadapted to the cross-sectional shape of the bore of the locking element.7. An assembly as defined in claim 6, wherein the guiding element isformed with a vertically extending slit in connection with the bore, theslit of the guiding element being closed by means of an end piece on theside that faces away from the bore.
 8. An assembly as defined in claim7, wherein the end piece of the slit of the guiding element is formedwith a vertically extending rupture line.
 9. An assembly as defined inclaim 6, wherein the locking element is formed with a recess adapted sothat the locking piece of the connecting element may be passed from thebore of the guiding element and into the bore of the locking element,and which extends between the bores of the guiding and locking elements.10. An assembly as defined in claim 9, wherein the locking element isformed with a guide surface adapted so that the connecting element maybe displaced into the slit of the guiding element, and the locking pieceis brought into engagement with the bore of the locking element, theguide surface being located in association with the recess and the boreof the locking element.
 11. An assembly as defined in claim 6, whereinthe connecting element is connected to the anchor tether by ashackle-like securing member.
 12. An assembly as defined in claim 6,wherein a portion of the anchor tether is coiled up and fixed by alashing, arranged so that it may break into pieces on the occurrence ofwave heave during the connecting of the suction anchor and the anchortether.
 13. An assembly as defined in claim 6, wherein the anchor tetherincludes a chain.
 14. A method of placing a suction anchor with anattached tether on the ocean bed, including lowering the suction anchorand securing the anchor by suction to the ocean bed, and thereafterconnecting a lower end of the anchor tether to the suction anchor, themethod comprising: lowering the lower end of the anchor tether into avertically extending guiding element with a lower locking element, theguiding and locking elements being formed with a bore and arranged sothat the longitudinal axes form an acute angle, the lower end of theanchor tether having an elongate connecting element; pulling an upperend of the connecting element outwards from the suction anchor so thatthe connecting element is brought into a position in which thelongitudinal axis of the connecting element is generally concentric withthe longitudinal axis of the locking element; and pulling the connectingelement outwards from the suction anchor and toward the longitudinalaxis of the bore of the locking element until the connecting elementengages the locking element of the suction anchor, the connectingelement including a locking piece with a cross-sectional shape adaptedto the bore of the locking element.
 15. A method as defined in claim 14,wherein when the locking piece is lowered into the locking element, theconnecting element is displaced sideways out from the suction anchor andinto a slit formed in the guiding element.
 16. A method as defined inclaim 15, wherein the locking element includes a guide surface for thelocking piece.
 17. A method as defined in claim 14, wherein when theupper end of the connecting element is pulled outwards from the suctionanchor, the connecting element is torn through an end piece of a slit ofthe guiding element, the end piece being formed with a verticallyextending rupture line.
 18. A method as defined in claim 14, whereinwhen the upper end of the connection element is pulled outwards from thesuction anchor, the locking piece is retained in the locking element,parts of the locking piece first bearing on the guide surface of thelocking element and then on parts of the bore of the locking element.19. A method as defined in claim 14, wherein a portion of the anchortether is coiled up and fixed by lashing arranged to break into pieceson the occurrence of wave heave when connecting the suction anchor andthe anchor tether.